168 Excel Sheet Column Title

Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB 

class Solution {
public:
    string convertToTitle(int n) {
        if(n < 1)
            return "";
        else
        {
           string result="";
           while(n){
                n--;
                char c= n%26+'A';
                result=c+result;
                n/=26;
           }
           return result;
        }
    }
};

注意几个问题；

1 数字转字符时候先--。

2 string += 顺序问题。